Riboflavin is the precursor of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), coenzymes required for the activity of flavoenzymes involved in the transfer of electrons in oxidation-reduction reactions. Flavins are light sensitive and rapidly degrade when exposed to light in the near ultraviolet and visible wavelengths. Some of the byproducts of flavin photodegradation are toxic. A quantitative survey of flavins in rabbit ocular tissues is reported. Adult male Dutch-Belt Rabbits were fed purified diets containing 3, 30, or 300 mg riboflavin/kg for 1 month. A method of aqueous extraction and high-performance liquid chromatography with fluorescence detection was used to measure riboflavin, FMN, and FAD in cornea, lens cortex, lens nucleus, retina, and blood. The retina contained the highest flavin concentration. In all tissues, the primary flavin was FAD followed by FMN and riboflavin. The highest concentration of riboflavin occurred in the cornea followed by the retina, lens cortex, and lens nucleus. A trend toward increasing concentrations of riboflavin occurred in the retina and blood in response to excess dietary riboflavin, but the concentration changes were not statistically significant. The highest concentration of FAD and FMN occurred in the retina followed by the cornea and the lens cortex and nucleus. The relative contribution of riboflavin, FMN, and FAD to the total flavin pool was markedly different in the various tissues of the eye. The proportion of tissue flavins present as riboflavin decreased from anterior to posterior. It was highest in the cornea followed by lens and retina. The pattern of distribution for FMN was: cornea greater than retina greater than lens cortex and nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)